Stitching with the 40/4

The Hartblei 40/4 offers an intriguing advantage for making higher resolution stitched images: a tripod mount which keeps the lens in a fixed position, thus eliminating parallax caused by the lens being moved during a shift (the camera moves instead).

In fact, the Hartblei 40/4 is the only shift lens available today that has a tripod mount. The tripod mount is also a near-necessity, given the weight of the lens (1706g = 3 pounds 12 ounces); stressing the lens mount with the weight of the lens and the torque of shift or tilt isn’t a good idea.

While desirable, the tripod mount has a downside: there is no straightforward way to do a center/left/right stitched image, since the shift mechanism is unidirectional. However, with the lens fixed on the tripod, one can press the rotation-release lever on the lens, which allows the camera to rotate by 180°. The trick is getting 180°, instead of 170° or 185° (or whatever). It’s doable, but far from ideal. Alternative designs which allow left/right bi-directional shifting do not have this issues.

Sharpness

While the other examples recommend f/11 as the best choice overall, this image was shot at f/8 in the hope that it would be adequate given the subject distance. And indeed it is, except for one troublesome issue: shifting the lens causes the focus to be move slightly in the shifted frame, dropping peak sharpness—an incentive to stop down to f/11 or f/16. The workaround is to focus after making the shift movement, just fine for single-frame images, but for stitching it’s extra work.

The unshifted frame shows very good sharpness and contrast. The shifted frame should be identical, but it has gone slightly soft at the point of focus. Examination of the foreground shows that focus has moved slightly forward.

This behavior must be understood in context: readers of my review of the Zeiss ZF 21/2.8 Distagon know just how troublesome exact alignment can be, across a variety of lenses. With the complex mechanics of a shift lens, it’s probably not realistic to expect perfect alignment through the range of movements, where 10 microns is more than enough to visibly impact image sharpness.

Central area (focus variance)

The two crops below were taken from center of the frame; this was the point of focus.

Observe how sharpness has declined in the shifted frame; the focus has moved slightly. This indicates a mechanically-induced focus variance, probably only 10-20 microns, but enough to affect the sharpness.

Actual pixels, unshifted frame

Actual pixels, shifted frame

Foreground (focus variance)

These two crops were also taken in the foreground area. The shifted frame is slightly sharper, confirming that focus has moved slightly forward.

Actual pixels, unshifted frame

Actual pixels, shifted frame

Conclusions

While overall imaging performance is very high, with especially appealing color, attention must be made to subtle shifts in focus when shift is applied. This makes the Hartblei 40/4 less than ideal for quick shift-lens-stitching applications.